Pulmonary function tests are confusing to many patients. And, as those with heart disease are usually aware of their blood pressure and cholesterol levels, the importance of knowing your numbers when it comes to pulmonary function tests (PFTs) and COPD is commonly overlooked.
The National Lung Health Education Program is currently on a mission to encourage patients to be aware of their pulmonary function test results by focusing on their mantra "test your lungs; know your numbers." Their mission also includes increasing the percentage of doctors who use spirometers in general practice, as it is currently reported that only 30% are doing so at this time.
Knowing your numbers is just another way for you to be your own patient advocate when it comes to your health. It also gives you a method of comparison to determine how well you are responding to treatment and if your disease is progressing.
Purpose of Pulmonary Function Tests
In the diagnoses of COPD, pulmonary function tests are performed to assess lung function and determine the degree of damage to the lungs. Along with patient history, lung imaging studies and open lung biopsy, PFTs have become important for doctors in the evaluation of respiratory health.
Pulmonary function tests can be used for a number of reasons:
- Screening for the existence of lung diseases
- Determining the patient's condition prior to surgery to assess the risk of respiratory complications after surgery.
- Evaluating the ability for a patient to be weaned from a ventilator
- Assessing the progression of lung disease and the effectiveness of treatment
Three types of pulmonary function tests are used in the diagnosis of COPD - spirometry testing, diffusion studies and body plethysmography.
Spirometry Testing
The most commonly used device for lung function screening, this hand-held device can easily be used by patients with the assistance of an experienced technician. It is normally the clinician's first choice when attempting to diagnose a respiratory problem. A convenient, noninvasive procedure, spirometry can be performed in the privacy of your doctor's office or any inpatient or outpatient facility.
Spirometry requires the patient, after all air has been expelled, to inhale deeply. This maneuver is then followed by a rapid exhalation so that all the air is exhausted from the lungs.
Results of spirometry tests vary, but are based on predicted values of a standardized, healthy population.
COPD causes the air in the lungs to be exhaled at a slower rate and in a smaller amount compared to a normal, healthy person. The amount of air in the lungs will not be readily exhaled due to either a physical obstruction (such as with mucus production) or airway narrowing caused by chronic inflammation.¡±
Common Terminology of Spirometry Tests Critical in Diagnosing COPD
- VC-Vital Capacity - The amount of air that can be forcibly exhaled from your lungs after a full inhalation.
- FVC-Forced Vital Capacity - The amount of air which can be forcibly exhaled from the lungs after taking the deepest breath possible.
- FEV1-Forced Expiratory Volume in One Second - The amount of air which can be forcibly exhaled from the lungs in the first second of a forced exhalation.
- FEV1/FVC-FEV1-Percent (FEV1%) - The ratio of FEV1 to FVC and tells the clinician what percentage of the total amount of air is exhaled from the lungs during the first second of forced exhalation.
- PEFR Peak Expiratory Flow Rate- Measures if treatment is effective in improving airway diseases such as COPD.
- FEF-Forced Expiratory Flow - A measure of how much air can be exhaled from the lungs. It is an indicator of large airway obstruction.
- MVV-Maximal Voluntary Ventilation - A value determined by having the patient inhale and exhale as rapidly and fully as possible in 12 seconds. The results reflect the status of the muscles used for breathing, how stiff the lungs are and if there is any resistance in the airways when breathing. This test tells surgeons how strong a patient's lungs are prior to surgery. If patients demonstrate poor performance on this test, it suggests to the doctor that respiratory complications may occur after surgery.
What Do the Numbers Mean?
Doctors also use spirometry testing to evaluate the severity of COPD. Your test results will be compared with tables of normal values that use variables such as age, gender, body size and race as a method of standardization.
With spirometry, test results will usually be measured twice, both before and after you are given a bronchodilator. If there is an improvement in two of three measurements, this means you will respond well to treatment.
Although there are a number of systems to choose from, the following is the method recommended by the Global Initiative for Obstructive Lung Disease (GOLD):
| GOLD Spirometric Criteria for COPD Severity | ||
| I. Mild COPD | * FEV1/FVC < 0.7 * FEV1 >/= 80% predicted | At this stage, the patient is probably unaware that lung function is starting to decline |
| II. Moderate COPD | * FEV1/FVC < 0.7 * 50% </= FEV1 < 80% predicted | Symptoms during this stage progress, with shortness of breath developing upon exertion. |
| III. Severe COPD | * FEV1/FVC < 0.7 * 30% </= FEV1 < 50% predicted | Shortness of breath becomes worse at this stage and COPD exacerbations are common. |
| IV. Very Severe COPD | * FEV1/FVC < 0.7 * FEV1 < 30% predicted or FEV1 < 50% predicted with chronic respiratory failure | Quality of life at this stage is gravely impaired. COPD exacerbations can be life threatening. |
